jamesjedi

I am not sure that I did the leak down correct. I will try it again in the morning. I did a compression test, and the results were just over 150 for three cylinders, and 60 for cylinder #1.

I help is great...Thanks

Oddjob

I assume that it is a running motor?

If you have 100% leakdown on two cylinders, that means zero compression and the motor would not run or start. The cylinder with 60 psi compression should show some significant leakdown, but the only way to have 100% leakdown is if a valve is gone or the rings are missing, hole in a piston, etc. A leaking headgasket will show very little on a leakdown, maybe only a few %.

Must have setup the tester incorrectly.

944Ross

He switched to a compression test there; he's talking psi, not % leakdown. Sounds like a bent or burned valve with those numbers.

67King

You did it wrong. You have to be sure it as at TDC with both valves closed, which is between the compression and power strokes. You did it between the exhaust and intake strokes, when both valves are likely open. Wait, is your cam installed, or not? You can't do a compression test without it, but you had earlier said it was off?

To the guy that said TDC because cylinder pressures are higher, that is not true. On a leakdown test, you control the air pressure in teh cylinder. It doesn't matter where the piston is.

If the cam is out, do it at BDC, it is less dangerous. At TDC, it doesn't take much to have the crank rotate over. If you are holding it with something, it is a good way to break things. Like fingers.

jamesjedi

Well.. we are always learning. I did it wrong. Very wrong. I was reversing the cylinder numbers, I was counting the cylinder closest to the passenger compartment as number 1, when it is actually number 4. I believe I now am doing it correct. These are the numbers;

Compression

1 178
2 168
3 170
4 78


Leak Down

1 16%
2 16%
3 14%
4 70 %

When number 4 was leak tested, there was considerable air escaping from the air flow meter area. If I did not mention it, the car runs.


Thanks for any help.

James

Mike C.

Ha ha! that would do it... In regards to piston position (with valves closed), the idea that it could make some difference due to differing cylinder wear/distortion from bottom to top seems reasonable. I'd sure like to see some data.

jamesjedi

I would not go by any of the result that I first posted. I have no idea f any were going to give you an accurate answer.

Hopfully I can get some insight into the more accurate numbers that I have for compression and leak down. On a side note, you need a good compressor to a leak test.

jamesjedi

Is it safe to assume that the intake valve is stuck? The engine problems happened when I was at the track. Possibly over revving? Is the compression test indicative of bigger problems?

Thanks for any help.

John_AZ

Stuck, Probably not. Burnt, fried, toasted, yes. Maybe the valve seat is damaged beyond repair. Valve quides bad.

Check with a machine shop for price on head machine work and add the cost for 1 or 2 valves. Maybe get a rebuilt head??

GL
John

jamesjedi

I have already sourced a reconditioned head. I am wondering what caused the oil to be on all of the spark plugs? Is it likely that there is more going on?

M758

Ok seems like leaking in take valve on #4. Both compression and leakdown show that. The car will still run like that, but not very well. need to remove the head to fix it.

BTW... an overrev due hitting the wrong gear on track can bend valves. I have seen it where guys hit 3rd instead of 5th at 100 mph and bend valves. You won't bend valves over reving to 7500 rpm, but can at 9000+ when you get the wrong gear. It could be that you only bent one valve to as which valve floats depends on the lifters.

jamesjedi

I just picked up a 951 head that has a 3 way grind. I will put it on tomorrow afternoon with a turbo head gasket.

I have been wondering if I should remove my chip to help reduce the chances of bending valves? I am not sure if this would help the motor last longer?

Mike C.

No need to worry. Unlike engines with variable valve timing, the relative positions of pistons and valves is controlled by the cam belt alone. The chip only changes when the spark if fired and how long the fuel injector stays open (fuel metering).

jamesjedi

Does it not increase the rev limiter? If so, perhaps this caused my valves to be bent.

John_AZ

Is the car you are working on your '86 NA?

There have been a few posts on using the 951 turbo head with ceramic liners on a NA. Maybe someone else can comment. I think it has something to do with the decreased air flow which is required for the turbo intake---not sure.

John